1. Field of the Invention
The present invention relates to a vacuum heat insulating material used for a refrigerator, a refrigerator truck and so on.
2. Description of Related Art
A related-art vacuum heat insulating material is fabricated by covering a core material formed of glass wool and the like with an outer covering material formed of a gas barrier film to thereby decompress and seal the inside. Most of the vacuum insulating materials have a flat plate shape with a thickness of 3 mm to 20 mm and are applied to products such as the refrigerator in the original shape mainly under the circumstances of the fabricating method and the reliability. In order to improve heat insulating characteristics of the heat insulating material, it is important to use a substance to which heat is hardly transferred as a constituent material, to reduce the contact area between materials and to control the heat transfer to a direction of a surface perpendicular to the heat insulating direction for suppressing conduction and radiation of heat.
As application examples of the vacuum heat insulating material, an example in which fibers are arranged perpendicular to the heat insulating direction to suppress the heat conduction amount (for example, refer to JP-A-60-208696 (Patent Document 1)), an example in which a metal foil or a metal deposition film having an excellent effect of blocking the radiation heat is buried (for example, refer to JP-A-62-13979 (Patent Document 2)), an example in which a plate-like substance such as mica having an excellent effect of blocking the radiation heat is integrated with a core material such as a glass mat by a resin and stacked in a plane (for example, refer to JP-A-10-238938 (Patent Document 3)) can be cited. In Patent Document 3, a composite material in which the plate-like substance is laminated in the surface direction is formed by uniformly dispersing a slurry liquid on the glass mat, in which the plate-like substance such as mica having the excellent effect of blocking the radiation heat is dispersed.
Apart to be insulated is not always a flat surface shape. When there is a corner part, a protrusion or a step in the part to be insulated, there is known a method in which processing such as bending, drilling and so on is performed in the vacuum heat insulating material, and the shape of the outer covering material is previously formed to allow the shape of the vacuum heat insulating material to correspond to the shape of the part to be insulated. As forming methods, there are a method in which a bag-shaped outer shell material houses a powdered or granular filler, the top and bottom of the outer shell material are compressed by using a die having a convex portion, and the inside of the outer shell material is evacuated to thereby form a concave portion in the surface (for example, refer to JP-A-61-168772 (Patent Document 4), and a method in which the inside of a film container filled with a heat insulating material is decompressed, a plate-shaped vacuum heat insulating material fabricated in a sealed state by heat sealing is molded in a decompressed state in a vacuum container, and the pressure is returned to a normal pressure while holding the material (for example, refer to JP-A-63-163764 (Patent Document 5).